He said that inspectors need to gather enough evidence to show that individuals are breaking the law, but their efforts are hampered by a lack of powers and poorly worded legislation.

“We are really frustrated,” he said. “There are a number of things. I don't have powers to force entry. So in those very rare occasions where children are at risk and I need to get in there...I can't, I have to phone the police and they may well be busy doing other things.”

Mr Coffey said on one occasion, he accompanied a team of inspectors to a suspected illegal school, and only after breaking in could they discover the extent of the horrifying conditions.

In January 2016, the Department for Education set up a special task force dedicated to investigating illegal schoolsCredit:
David Davies

“We went into this school, we had to break in with the police so we smashed our way in,” he said.

“This is where we saw filthy, dirty beds and mattresses on floors, we saw absolute segregation, barred up windows, no running water in toilets. Just filthy, dirty conditions.

“Some of these things are really frustrating, and some of my inspectors go and see this stuff and get really upset. It's shocking, some of it it really is dreadfully shocking. And we need to stop that from happening.”

Mr Coffey, who manages all of Ofsted’s operations across the country, said that inspectors need the powers to enter related premises, since illegal schools often have an “escape route” to a nearby building.

“If we are really worried about where [children] are, but we know that the owner of the building we are in owns the building next door...I don't have the investigative powers to go next door.

“That can be a source of frustration because people can jump from one building to another very, very quickly, especially if they have basements with interconnecting doors - I have seen some of that.”

Mr Coffey said that inspectors are also held back by their inability to seize evidence. “We have the power to photocopy evidence and that's great if there is a photocopier available - but some of these places don't have photocopiers.

“So we are having to use phones to take screenshots of some of the dreadful literature about the role of men and women in society and [the way] women should be treated, and some really difficult things.”

Mr Coffey said that the Education and Skills Act 2008 - which gives Ofsted the power to inspect suspected unregistered schools - was introduced with “good intentions” but that it is too vague.

“I have got to be honest the law doesn’t really help us here,” he said. “This is why we haven't brought a successful prosecution yet, because the law is a little bit unclear… a little bit flimsy.

“It talks about what constitutes an unregistered school. But it doesn't define an ‘education’, it doesn’t define a ‘school’ and it doesn't define ‘full time’.”

It's shocking, some of it it really is dreadfully shocking. And we need to stop that from happeningMatthew Coffey

In January 2016, the Department for Education set up a special task force dedicated to investigating illegal schools.

The taskforce has so far identified 291 suspected unregistered schools and issued warning notices to 38 schools which it suspects are operating illegally.

Since then, 27 have ceased operating illegally while 11 remain under criminal investigation. Inspection summary logs, seen by The Sunday Telegraph, reveal that a relatively high proportion of suspected illegal institutions are faith schools.

Of the nine suspected illegal settings which have been served a warning notice by Ofsted in the West Midlands, three are Islamic.

Safeguarding concerns noted by inspectors for these schools include “dilapidated buildings” and “incomplete DBS checks”. Out of 12 suspected illegal schools in London, four are Jewish and one is Islamic.

Inspectors noted “broken windows and dilapidation” at the schools, and that “pupils had no access to clean drinking water inside the building”. The logs showed that “pupils expressed wish they were at a ‘normal’ school.”

“I would regard my time there as child abuse,” he said. “The worst aspect was definitely the hitting. I was cheeky so I was hit a lot. A wooden cooking spoon was always on the table and it was used daily.”

Earlier this week, Ofsted's chief inspector Amanda Spielman warned that unregistered school "hide from the rule of law".

Speaking at the Birmingham Education Partnership conference on Friday, she said they are often found in "buildings that wouldn’t pass the most basic of health and safety checks".

"Some of the images taken by inspectors that I have seen show places that are filthy and downright dangerous. In short, they put children at risk," she added.

A Department for Education spokesperson said: “Unregistered schools are illegal and unsafe. We have given Ofsted additional resources to root out these settings, step up investigations and work with us to take whatever action is required, including closing down a school or working with the police and Crown Prosecution Service as necessary.‎

“We will not hesitate to take action where children are being put at

risk or not receiving a suitable education, by working with local authorities and the police who have clear powers to intervene where necessary. We expect them to make use of these powers and will support them to do so.”